This thread is intended to be a place for cool things that you just found out about, but that aren't necessarily major enough to merit their own thread.
For instance, today I learned why heavy water is/was used as a moderator in certain types of reactors. Since hydrogen atoms are small, they are very good at slowing down neutrons, but regular hydrogen also has a nasty tendency to absorb said neutrons (which you probably want to be absorbed by the uranium/plutonium in your reactor). Deuterium is a bit heavier, but still pretty damn good at slowing neutrons, and it's much less likely to absorb them.

Had a solid day at Gore today, bit annoyed that some of the stuff they said was going to open didn't. Snow was pretty good quality though, and they're working pretty hard at making more (did run into the problem of skiing on a trail with ongoing snowmaking and having my goggles ice up pretty bad).
Did run into the problem of having people in the group with different stamina/skill levels. Our group of 7 people ended up split into 2 or 3 groups the whole day.

This is the official thread for discussion of anything related to skiing/snowboarding on SH. If you like throwing yourself down a frozen mountain, or are at all interested, this is the place.
My personal experience: I mostly ski in the northeast (New York / Vermont), have never tried snowboarding. All my experience is at resorts, so if you want to know more about crazy backcountry shit I might not be able to answer 100% (though I am seriously considering heading to Tuckerman Ravine this year).
Basic advice:
Wear a helmet
Rating systems are uniform everywhere, what's a black diamond somewhere might be a blue at a more hardcore place. Anything above black diamond (and especially above double black) is as much marketing as difficulty rating.
Difficulty depends on conditions
Wear a helmet
Taking a lesson your first time is probably a good idea
Make sure your boots are properly fitted
Resources:
http://www.skibum.net/
Site with a bunch of general info about skiing, and has little blurbs/ratings about a whole lot of American ski/snowboard places, grouped by state (surprised how many midwest states have ski places). Has a pro-ski / anti-snowboard tilt.
https://www.liftopia.com/
Deals on lift tickets (it is an expensive hobby, especially if you go to Aspen or Vail)
http://nyskiblog.com/
Blog about New York skiing
http://forums.alpinezone.com/forumdisplay.php/10-Northeast-Skiing-and-Snowboarding-Forum
Forum about skiing in the Northeast
https://www.tetongravity.com/forums/
General skiing forum, but has more of a western audience. Also appears to have a vibrant shitposting culture.
http://mountainvertical.com/
Shows de-marketified vertical ratings for each mountain. Vertical (distance from top to bottom) is a big deal for marketing, and there's a lot of ways to fudge it.
http://www.goremountain.com/
http://www.whiteface.com/
The two places I go most often. Whiteface has more vertical and longer runs, but is farther away and is often windy and iced over. Gore is closer, less crowded, and sometimes has better conditions.
http://timefortuckerman.com/
Site about Tuckerman Ravine, one of the holy sites of Northeast skiing.
https://www.youtube.com/channel/UCzmlnH8vDQHoEb2TrC0WDCg
Jerry of the Day
Pic at the top is from the summit of Whiteface about a year ago.

One of the many issues facing nuclear power in the US is economics. Once operational, nuclear energy is quite cheap in terms of $/MWh. However, the startup costs are enormous, which results in the overall cost of power going up. In an environment like today, where there's cheaply available natural gas, nuclear power becomes quite unattractive, especially with all the extra taxes levied on it and public fears.
This article has some good info; http://www.world-nuclear.org/information-library/economic-aspects/economics-of-nuclear-power.aspx
One interesting aspect which I first heard today is that the inclusion of renewables in the energy grid hurts nuclear energy. Nuclear plants are best run at a steady power level, providing base load. However, renewables such as wind and solar provide wildly varying amounts of power depending on the weather conditions or time or day. As a result, the nuclear plant is forced to vary its power level, running less efficiently. For reasons that I'm not 100% sure of, gas and coal plants can respond to variations in base load better, and so are more economic.
There's a couple ways I could think of to get around this. One is mass production of standardized reactor designs, I believe there's already been a lot of work on that front. Another is putting multiple reactors in the same plant; that article I linked says the Chinese estimate you get a 15% cost reduction (in $/MWh) by putting two reactors on the same site instead of separately.
I also heard that before building wind and solar was the cool thing to do to score political points, hydro and geothermal were the big renewable energy sources. Because they were economically viable, not because of hippies. Hydro being economically viable is obvious, but I'm more curious about geothermal. It seems like a pretty good energy source to use (where available).

This seems like something that should be revisited now since automatic systems are significantly more advanced than when the regulation was presumably first written (a cursory search doesn't reveal when that section of 10 CFR 50 was enacted). Appropriately tested software monitored by an operator should be sufficient for civilian applications.

Very detailed report from MIT on the use of nuclear in low carbon energy infrastructure; http://energy.mit.edu/research/future-nuclear-energy-carbon-constrained-world/
TL;DR Nuclear becomes more attractive the more you reduce your emissions goals (in terms of kgCO2/kW)

Good looking boats, and it seems that they're also using modular construction like the Virginias (I assume the Russians and Chinese build modular also, but I don't know offhand).
Are they still fucking around with low-enriched reactors for some dumb reason?

This thread is for discussion of modern (including Cold War) tank destroyer and gun carrier concepts. Most of these feature a good sized gun on a relatively light chassis with good mobility (as a result, they are sometimes known as light tanks). Some are built on converted IFV chassis. Examples include;

https://aviation-safety.net/wikibase/wiki.php?id=217634
ERJ-190 flight controls don't work, plane flails around uncontrollably for a while.
They did manage to land safely, and it looks like they did a decent job resolving the problem.

For discussion stupid shit like Pinnacle 3701 and this: http://www.rapp.org/archives/2015/12/normalization-of-deviance/ For reference, here's what a gust lock looks like on a Cessna 172; As you can see, it's essentially a pin that goes in the control column and keeps it from moving. Even starting the airplane with this installed would be utterly ludicrous to me, as would not doing the checklist. If your car runs out of oil in the middle of a drive you're going to have a bad day and engine repair bill, if your plane runs out of oil muffling there's a good chance you're going to turn yourself into chunky salsa on the side of a mountain.

Backstory (skip if you don't like alternate history junk)
The year is 2239. It has been roughly 210 years since the world was engulfed in nuclear war. Following the war, the United States splintered into hundreds of small statelets. While much knowledge was retained in some form (mostly through books and other printed media), the loss of population and destruction of industrial capability set back society immensely.
Though the Pacific Northwest was less badly hit than other areas, the destruction of Seattle and Portland, coupled with the rupturing of the Cascadia Subduction Zone in 2043, caused society to regress to a mid-19th century technology level. However, in the early 2100s, the Cascade Republic formed, centered near Tacoma. The new nation grew rapidly, expanding to encompass most of Washington and Oregon by 2239. The Cascade Republic now extends from the Klamath River in the south to the Fraser River in the north, and from the Pacific roughly to central Idaho. Over time, the standard of living and industrial development improved (initially through salvaging of surviving equipment, by the late 2100s through new development); the population has grown to about 4.5 million (comparable to 1950 levels), and technology is at about a 1940 level. Automobiles are common, aircraft are less common, but not rare by any means. Computers are nonexistent aside from a few experimental devices; while scientists and engineers are aware of the principles behind microchips and other advanced electronics, the facilities to produce such components simply do not exist. Low rate production of early transistors recently restarted.
The current armored force of the Cascade Republic consists of three armored brigades. They are presently equipped with domestically produced light tanks, dating to the 2190s. Weighing roughly 12 tons and armed with a 40mm gun, they represented the apex of the Cascade Republic's industrial capabilities at the time. And when they were built, they were sufficient for duties such as pacifying survivalist enclaves in remote areas. However, since that time, the geopolitical situation has complicated significantly. There are two main opponents the Cascade Republic's military could expect to face in the near future.
The first is California. The state of California was hit particularly hard by the nuclear exchange. However, in 2160, several small polities in the southern part of the state near the ruins of Los Angeles unified. Adopting an ideology not unfamiliar to North Korea, the new state declared itself the successor to the legacy of California, and set about forcibly annexing the rest of the state. It took them less than 50 years to unite the rest of California, and spread into parts of Arizona and northern Mexico. While California's expansion stopped at the Klamath River for now, this is only due to poor supply lines and the desire to engage easier targets. (California's northward advanced did provide the final impetus for the last statelets in south Oregon to unify with the Cascade Republic voluntarily).
California is heavily industrialized, possessing significant air, naval, and armored capabilities. Their technology level is comparable to the Cascade Republic's, but their superior industrial capabilities and population mean that they can produce larger vehicles in greater quantity than other countries. Intelligence shows they have vehicles weighing up to 50 tons with 3 inches of armor, though most of their tanks are much lighter.
The expected frontlines for an engagement with the Californian military would be the coastal regions in southern Oregon. Advancing up the coastal roads would allow California to capture the most populated and industrialized regions of the Cascade Republic if they advanced far enough north. Fortunately, the terrain near the border is very difficult and favors the defender;
(near the Californian border)
The other opponent is Deseret, a Mormon theocratic state centered in Utah, and encompassing much of Nevada, western Colorado, and southern Idaho. Recently, tension has arisen with the Cascade Republic over two main issues. The first is the poorly defined border in Eastern Oregon / Northern Nevada; the old state boundary is virtually meaningless, and though the area is sparsely populated, it does represent a significant land area, with grazing and water resources. The more recent flashpoint is the Cascade Republic's recent annexation of Arco and the area to the east. Deseret historically regarded Idaho as being within its sphere of influence, and maintained several puppet states in the area (the largest being centered in Idaho Falls). They regard the annexation of a signficant (in terms of land area, not population) portion of Idaho as a major intrusion into their rightful territory. That the Cascade Republic has repaired the rail line leading to the old Naval Reactors Facility, and set up a significant military base there only makes the situation worse.
Deseret's military is light and heavily focused on mobile operations. Though they are less heavily mechanized than the Cascade Republic's forces, operating mostly armored cars and cavalry, they still represent a significant threat to supply and communication lines in the open terrain of eastern Oregon / southern Idaho.
(a butte in the disputed region of Idaho, near Arco)
Requirements
As the head of a design team in the Cascade Republic military, you have been requested to design a new tank according to one of two specifications (or both if you so desire):
Medium / Heavy Tank
Weight: No more than 45 tons
Width: No more than 10.8 feet (3.25 meters)
Upper glacis / frontal turret armor of at least 3 in (76mm) LoS thickness
Side armor at least 1in (25mm) thick (i.e. resistant to HMG fire)
Power/weight ratio of at least 10 hp / ton
No more than 6 crew members
Primary armament capable of utilizing both anti-armor and high explosive rounds
Light tank
Weight: No more than 25 tons
Width: No more than 10.8 feet
Upper glacis / frontal turret armor of at least 1 in thickness
Side armor of at least 3/8 in (10mm) thickness
Power/weight ratio of at least 12 hp / ton
No more than 6 crew members
Primary armament capable of utilizing both anti-armor and high explosive rounds
Other relevant information:
Any tank should be designed to operate against either of the Cascade Republic's likely opponents (California or Deseret)
The primary heavy machine gun is the M2, the primary medium machine gun is the M240. Use of one or both of these as coaxial and/or secondary armament is encouraged.
The secret archives of the Cascade Republic are available for your use. Sadly, there are no running prewar armored vehicles, the best are some rusted hulks that have long been stripped of usable equipment. (Lima Tank Plant ate a 500 kt ground burst)
Both HEAT and APFSDS rounds are in testing. APCR is the primary anti-armor round of the Cascade Republic.
Either diesel or gasoline engines are acceptable, the Cascade Republic is friendly with oil producing regions in Canada (OOC: Engines are at about a late 1940s/early 50s tech level)
The adaptability of the tank to other variants (such as SPAA, SPG, recovery vehicle, etc.) is preferred but not the primary metric that will be used to decide on a design.
Ease of maintenance in the field is highly important.
Any designs produced will be compared against the M4 Sherman and M3 Stuart (for medium/heavy and light tank), as these blueprints are readily available, and these tanks are well within the Cascade Republic's manufacturing capabilities.

There's a shitload of real estate in the solar system, and we don't know much about most of it. What unmanned probes would you like to see built to learn more about the planets and other objects?
My first choice is an Enceladus orbiter/lander; it's one of the best candidates for extraterrestial life, has confirmed cryovolcanism, and organics have been found near it. Plus, any mission you send there can get some bonus science of Titan and other cool places in the Saturn system.
I also like FOCAL, just for the sheer audacity of it.
https://en.wikipedia.org/wiki/FOCAL_(spacecraft)

BFR is now Starship (well, Super Heavy + Starship).
There is some concern over the number of changes BFR seems to be going through.
Regardless of whatever changes happen to the design, I am going to assume they will be keeping the 9m diameter, since they have already started cutting metal. Would be stupid to switch to completely new tooling at this point.